This invention relates to RF signal coupling devices, especially those used in a cable TV system, e.g., signal couplers and splitters. The invention is more particularly directed to a device employing alumina substrate on which capacitors and resistors are printed on a ceramic substrate with a ground pad serving as a grounded capacitor plate for the printed capacitors.
A broad-band signal-splitter which can be incorporated into the embodiments of this invention is described in U.S. Pat. No. 4,789,845. Other line splitters or signal splitters are described in U.S. Pat. Nos. 3,454,905; 3,349,345; 3,673,517; and 3,500,252. These devices invariably utilize capacitors, resistors and inductors. In all cases these involve discrete capacitors, resistors, and inductors. These items can be expensive, and can involve additional labor costs in assembly to the printed circuit board. Also, discrete capacitors and resistors have leads, and these items impose an inductive load on the coupling device, and limit bandwidth.
These signal splitters, directional couplers, and kindred devices are intended for use in a cable TV system, and should have a pass band broad enough to handle the entire band of TV broadcast and cable channels. That is, the device should have a passband from 5 MHz to 1000 MHz.
Typically, the conventional splitter or directional coupler has RF transformers attached onto a printed circuit board with the leads being soldered to a printed conductor that extends through holes in the laminate. A number of discrete capacitors, coils and resistors have to be soldered to the printed conductor on the board, or, just as often, have to be soldered directly onto a lead of the transformer. Consequently, with the conventional device, the pass band becomes somewhat limited, especially at the high end, and the overall performance is unsatisfactory because of stray inductances and capacitances that intensive to produce.